Harvesting energy from ambient vibrations to power devices is a promising way to rid them of power cables and batteries as well as decrease their power consumption and size. There has been an increased use of piezoelectric and piezoresistive materials in making of micro-harvesters. Micro-harvesters find their main application either as independent power sources or as active sensors.
Micro-electromechanical systems (MEMS) sensors convert applied pressure to electrical energy by capacitive and piezoresistive sensing mechanisms. Piezoresistive sensors have DC input, simple conditioning circuits and higher output in comparison to capacitive sensors. Piezoresistive devices include PMOS and NMOS field effect transistors, diodes, and simple p-type and n-type resistors.
Piezoelectric transistors PET have been produced in the art in which piezoelectric PE and piezoresistive PR material are used. PET generally is based on modulating resistance of a PR element with a PE element. That is, the PR element is programmable based on displacement of the PE element. The PET may be used as a switch device, for example, based on modulating the PR element from a low to a high resistive state or visa versa. In such PET devices, an electric field is applied to the PE element along the same direction as the resulting displacement of the PE element. Therefore, the piezoelectric material is electrically manipulated by use of an external power source to allow for electrically controlling the piezoresistor in the different devices.
There is a desire in the field for the development of sensors and sensing techniques to improve utilizing energy of surrounding sources and generate good quality sensory data in a cost efficient and durable fashion using easily accessible probing systems.